1. Field of the Invention
The invention relates to a picture coding apparatus and a decoding apparatus which, when a video signal is to be encoded and decoded for storage or transmission, can realize high efficiency coding, and also a high speed search or reproduction of excellent efficiency.
2. Related Art of the Invention
Recently, MPEG (Moving Picture Expert Group) which is an international standard is typical of video coding.
According to MPEG, intrapicture coding is first conducted, motion vectors of a P-frame or a B-frame are detected on the basis of the intrapicture-decoded picture (I-frame) corresponding to the coding, motion compensation prediction of the detected motion vectors is conducted based on the motion vectors, and a difference between a motion compensated picture obtained by the motion compensation and the picture to be encoded is encoded. Namely, MPEG is a coding method of the intrapicture/interpicture selection type in which the intrapicture-decoded picture and the intrapicture coding of the picture are combined with each other.
In a coding method of the intrapicture/interpicture selection type, in order to prevent error propagation from occurring or enable an encoded picture to be reproduced from the middle irrespective of the contents of a moving picture, intrapicture coding is conducted with a predetermined period. When a moving picture is to be subjected to high speed reproduction, therefore, only a picture which has undergone intrapicture coding is extracted and then decoded to obtain a reproduced picture.
FIG. 10 is a block diagram of a high-speed reproduction apparatus in which an intrapicture-coded picture is extracted and then decoded. In the figure, 1 designates a coded input signal, 2 designates intrapicture-coded picture extracting means, 3 designates an intrapicture-coded signal, 4 designates intrapicture-coded picture decoding means, and 5 designates a decoded output signal.
The operation of the thus configured high-speed reproduction apparatus will be described. The intrapicture-coded picture extracting means 2 extracts only a picture which has undergone intrapicture coding, from the coded input signal 1 which has been subjected to coding of the intrapicture/interpicture selection type, and outputs the intrapicture-coded signal 3. The intrapicture-coded picture decoding means 4 decodes the intrapicture-coded signal 3 and outputs the decoded output signal 5. In this way, high-speed reproduction is conducted by extracting only an intrapicture-coded picture and decoding it.
In the high-speed reproduction apparatus, however, a P-frame or B-frame cannot be used in high-speed reproduction unless a I-frame or P-frame which is to be referred is decoded. Consequently, it is difficult to produce a high-speed reproduction apparatus which can smoothly conduct high-speed reproduction.
Even when only a part of a picture is updated, moreover, the previous picture must be updated. This causes the amount of information to be processed for high-speed reproduction, to be increased.
Since reproduction is performed at fixed intervals, it is difficult to conduct high-speed reproduction or a high-speed scene search in accordance with a change in contents of a picture.
Coding of pixel value information for a conventional picture scene is conducted on a single layer. In other words, pixel value information of the whole contents of one scene of a picture are completed on a single layer, and coding is conducted on each of the pixel value information on the single layer. When pixel value information which is completed on a single layer is to be encoded, the need for efficiently conducting the coding is growingly increased.
However, conventional means for encoding pixel value information which is completed on a single layer has a problem in that, even when a pixel which is not required to be encoded exists in the single layer, coding must be conducted with considering the value of the pixel and therefore the amount of information to be encoded is increased so that the processing speed is reduced.